Power transmission



POWER TRANSMISSION Filed May 8, 1946 M KELLAR K. GRAHAM April 8, 1952 INVENTOR.

MACKELLAR K. GRAHAM BY W 14 /M ATTORNEY Patented Apr. 8, 1952 2,591,806 POWER TRANSMISSION MacKellar K. Graham, Detroit, Mich., assignor to Vickers Incorporated, Detroit, Mich., a corporation of Michigan Applicationlvlay 8, 1946, Serial No. 668,121

a 1 i This invention relates to power transmissions, particularly to those of the type comprising two or more fluid pressure energy translating devices, one of which may function as a pump and another as afluid motor. 5 In the drawing:

The invention is particularly concerned with Figure 1 is a diagrammatic view of the inproviding in a hydraulic system having a convention. v tinuously driven pump an improved simple and Figure 2 is a diagrammatic view of the ineconomical means of having a relief valve invention similar to that of Figure 1 but showing corporated in the system as a safety element for the parts thereof in a different position of op-. relieving the pump of excessive pressure flui'd eration. when a maximum predetermined pressure has Referring now to Figure 1, there is showna been reached in the system also perform the pump H] which is adapted to be continuously function of unloading the pump at a lower presdriven by a prime mover, not shown, and which sure than the maximum relief valve pressure. is connected to a tank I2 by means of a suction In aircraft" hydraulic systems where the pump conduit [4. A pump delivery conduit I6 is conis being driven continuously by the aircraft nected to pump I 0 incorporated in which is a engine it has been the practice to use an unbalanced type relief valve [8, a check valve loading valve to unburden the pump of all but and an accumulator 22 which is connected to slight loads when hydraulically actuated elements 20 conduit 16 by means of a branch conduit 24. such as the landing gear are not being operated. The relief valve I8 is comprised of a body 26f The unloading valve in such systems loads and having an inlet chamber 28 connected to the unloads the pump in response to predetermined pump delivery conduit I6. A main valve 30 pressure increases and decreases in an accumureciprocably mounted in the body is balanced & D d d e as to pressure forces in the inlet chamber 28 In addition tothe unloading valve a separate and a control chamber 32, the latter of which relief valve is always provided in such systems is in communication with the inlet chamber 28 which is responsive to a higher pressure than by means of a restricted passage 34 in the valvev the unloading valve and which is used only as an. The main valve is normally biased by a safety element in case the unloading valve 30 means of a spring 36 mounted in the control fails t0 p Insuch ystems some difficulty chamber 30 so as to closea seat 38 and block has been experienced with unloading valves communication between the inlet chamber 28 and. which fail to unload completely, that is they an exhaust port 40, the latter being connected are subject to hanging up or incomplete opto tank 12 by means of a by-pass conduit 42.. l eration after starting to unload the pump thus The pressure forces acting on main valve 30 Pl i a conti ous u den thereon. may become unbalanced by venting or bleeding It is an object of this invention to incorporate the control chamber 32 to tank [2. For this in a hydraulic system having a continuously purpose the pilot relief valve 44 normally biased,v driven-pump a pressure responsive relief valve to a position closing communication between ofjthe balanced type and a pressure actuated 40 the control chamber 32 and the exhaust port 4ll snap acting valve in such a manner that the by means of a spring 46 will open communicar lief v v wi l perf rm he bl function of tion therebetween when a predetermined maxi-- a e ef va ve a d O an u lo d v v mum safe pressure as determined by the resist- It is a further object of this invention to nce of spring 46 rises in the system. p vi y lic system having a con- A venting port 48 of relief valve l8 connected timlollsly driven D p p e esponsive relief to control chamber 32 is connected by means va ve of the balanced yp and a posi ive a d of a conduit 50 to a control port 52 of a positive snap acting pressure actuated valve in such a a and snap acting valve 54, also having a pressure manner that the relief valve will not only perport 56 conn ct d to the pump delivery con-s form the double function of a relief valve and 50 1 m; 5 by means of b h nd it 58 and a of a 'u lo d va ve but Which l p t venting port 60 connected to tank 12 by means therelief valve when acting as an unloading of a conduit 62. Communication between c valve from oscillating or hanging up and assure trol port 52 and venting port 60 is controlled positive unloading of .the pump. by a poppet valve 64 which is normally biased to Further objects and advantages of the present, close a seat 66 by means of a spring 6? the invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred form of;

7 Claims. (01.10342) the present invention is clearly shown.

resistance of which is adjustable to suit the needs of a plurality of hydraulic systems.

A spring retainer I also acts as a guide for proper seating of valve 64. A piston I2 reciprocably mounted in valve 54 and having a projection I4 extending into the seat 66 is responsive to predetermined increases of pressure in a chamber I6 in communication with port 56 to shift valve 64 to open seat 66 and responsive to predetermined pressure decreases in the same chamber permitting spring 68 and pressure fluid to shift the valve 64 to the closed position.

In operation, with the pump I0 running pres sure fluid is delivered by conduit I6 to the inlet chamber 28 of relief valve I8 and through check valve 20 to a part of the hydraulic system not shown and also to accumulator 22 and to the pressure port 56 of valve 54. When a predetermined pressure has arisen in accumulator 22 which is also present in chamber 76 of valve 54, piston I2 Will shift. It should be noted that the force opposing the movement of piston I2 up to the time of valve 64 opening seat 66 is a product of the area of the ball seat and pressure plus the resistance of spring 68.

Referring now to Figure 2 at the point that valve 64 is lifted slightly from seat 66 opening the same there is a sudden reduction of the total force opposing the movement of piston I2 because the-total pressure force on top of the ball suddenly drops by reason of port 52 being opened to port 60. Due to the fact that the same increasing pressure force has remained existent in chamber 16 the result is a rapid upward movement of piston I2 and consequently valve 64 opens seat 66 sufiiciently to connect port 52 to exhaust port 60and vent the control chamber 32 of relief valve I8 to tank I2.

During this operation pressure fluid from pump I8 had also been delivered by means of conduit I6 to the inlet chamber 28 of relief valve I8 and through the restricted passage 34 of main valve 30 to the control chamber 32 thereof and thus balance the pressure forces upon the valve 38 to permit the spring 36 to maintain valve 38 in the closed position blocking communication between the. inlet chamber 28 of valve I8 and exhaust port;

Pressure fluid entering the control chamber 32 by means of restricted passage 34 had also been delivered by means of vent port 48 of valve I8 and conduit 58 to control port 52 of valve 54 where communication with venting port 68 was blocked by means of valve 64 closing seat 66. However, with venting port 68 being open to port 52 when valve 64 was shifted suddenly and completely the control chamber 32 of valve I8 is also open to" tank I2 resulting in a sudden decrease in pressure in the control chamber 32 and permitting pressure fluid in inlet chamber 28 to shift main valve 38 so as to open the exhaust port 40 thereof to tank I2 and by-pass the com' plete flow of pump II] to tank I2.

Pressure fluid trapped in accumulator 22 by means of check valve 28 will maintain piston 12 to the position shown in Figure 2. Due to the fact that control chamber 32 is vented to tank I2 a pressure sufficient to create a force to overcome the slight resistance of spring 36 is the only load resistance imposed upon the pump I8.

' 'Upon a predetermined decrease in pressure in accumulator 22 also present in chamber I6 spring 68' of valve 54 will overcome the resultant force upon piston I2 and shift valve 64 toward the closed position. As valve 64 nears the completely closed position a sudden build up of pressure will take place on top of valve 64 due to the now restricted opening of seat 66 and aid spring 68 in suddenly and completely shifting valve 64 to close seat 66.

Once the valve 64 is suddenly seated so as to close communication between port 52 and exhaust port 68 of valve 54 the control chamber 32 of relief valve I8 is no longer open to tank I2 and consequently the pressure forces in inlet chamber 28 and control chamber 32 suddenly become balanced permitting spring 36 to shift main valve 30 to the closed position and close seat 38. Pressure fluid now delivered from pump III through delivery conduit I6 is again free to flow through inlet chamber 28 check valve 20 to accumulator 22 and to the system, not shown.

If for any reason piston I2 should become frozen, pilot valve 44 of relief valve I8, which is set to open control chamber 32 to exhaust port 48 thereof at a higher pressure than valve 64 of valve 54 is set to open port 52 to exhaust port thereof, will serve as a safety element in preventing extensive damage to the system. In such case when a predetermined. safe maximum pressure has been reached in the system as determined by spring 46 of relief valve I8, pilot valve 44 will open control chamber 32 to exhaust port 40. The pressure forces in inlet chamber 28 and control chamber 32 which had been balanced now become unbalanced and main valve 30 will shift so as to open seat 38 to exhaust port 40 and by-pass the complete flow of pump ID to tank I2.

However, in this case main valve 38 of relief valve I8 is merely serving as a safety element in relieving excessive pressure fluid from pump II) to tank I2 and a continuous predetermined pressure equal to the resistance of pilot valve spring 46 is necessary to maintain valve 44 in the open position. In the former case with valve I8 operating as an unloading valve pressure fluid trapped in accumulator 22 by means of check valve 28 and not pressure fluid being delivered I by pump I8 maintains control chamber 32 open to tank I2.

- It should be noted that because valve 64 is suddenly and completely vented to tank when a predetermined pressure has arisen in accumulator 22 that control chamber 32 of valve I8 is also suddenly and completely vented to tank and consequently main valve 38 is prevented from hanging up and will shift so as to completely unload pump I6. In addition, the snap action of valve 64 and the complete venting of control chamber 32' will prevent any oscillation of main valve 30 when relief valve I8 is operating as an unloading valve.

While the form of embodiment of the inven- 60 tion as herein disclosed constitutes a preferred to by-pass excessive pressure fluid, a valve having a control port connected to the control chamber of the relief valve, a pressure port, a venting port, a poppet valve for controlling communication between the control port and the venting. port including means biasing the valve to the closed communication position, and means responsive to predetermined pressure increases at the pressure port lower than the first mentioned pressure for shifting the poppet valve to open communication between the control port and the venting port thereby opening communication between the venting port and the control chamber of the relief valve for causing the pressure forces on the relief valve to become completely unbalancecl.

2. In combination with a'pressure relief valve of the type which is balanced as to opposing pressure forces and having a control chamber ventable at a predetermined pressure for unbalancing the pressure forces and causing the relief valve to by-pass excessive pressure fluid, a valve having a control port connected to the control chamber of the relief valve, a pressure port, a venting port, a valve seat between the control and venting ports, a poppet valve biased by pressure corresponding to that in the control chamber of the relief valve for normally closing the seat, resilient means also biasing the valve to close the seat, and means responsive to predetermined pressure increases at the pressure port lower than the first mentioned pressure for overcoming the pressure and resilient biasing forces, and shifting the poppet valve to connect the venting port with the control chamber of the relief valve, whereby the pressure forces on the relief valve become completely unbalanced.

3. In a hydraulic power transmission system having a fluid pump forming a source of pressure fluid and a pressure responsive relief valve of the type which is balanced as to opposing pressure forces and having a control chamber ventable at a predetermined pressure for unbalancing the pressure forces and causing the relief valve to bypass excessive pressure fluid, said transmission having sufl'lcient fluid capacity and elasticity of members under stress to provide an accumulator effect, the combination with said relief valve of snap-acting valve means connected to the control chamber of the relief valve, said snap acting valve means being operable to vent the control chamber in response to a predetermined pressure lower than the first mentioned pressure and causing the relief valve to unload the pump.

4. In a, hydraulic power transmission system having a pump forming a source of pressure fluid, an accumulator for storing pressure fluid, and a pressure responsive relief valve of the type which is balanced as to opposing pressure forces and having a control chamber ventable at a predetermined pressure zfor unbalancing the pressure forces and causing the relief valve to by-pass the pump, the combination with said relief valve of snap-acting valve means connected to the control chamber of the relief valve and to the accumulator, said snap acting valve means being operable to vent the control chamber in response to predetermined pressure increases in the accumulator lower than the first predetermined pressure and causing the relief valve to unload the pump.

5. In a hydraulic power transmission system having a pump forming a source of pressure fluid, an accumulator for storing pressure fluid, a pressure relief valve of the type which is balanced as to opposing pressure forces including a ventable control chamber, and a pilot relief valve operably connected to the control chamber and re sponsive at a predetermined pressure for venting the control chamber thereby unbalancing the pressure forces and causing the relief valve to bypass the pump, the combination with said relief valve and pilot valve of an auxiliary pressure re sponsive valve connected to the control chamber of the relief valve and to the accumulator, said auxiliary valve being operable to vent the control chamber in response to predetermined pressure increases in the accumulator lower than the pilot relief valve predetermined responsive pressure and. causing the relief valve to unload the pump.

6. In a hydraulic power transmission system having apump forming a source of pressure fluid, an accumulator for storing pressure fluid, a pressure relief valve of the type which is balanced as to opposing pressure forces including a ventable control chamber, and a pilot relief valve operably connected to the control chamber and responsive at a predetermined pressure for venting the control chamber thereby unbalancing the pressure forces and causing the relief valve to bypass the pump, the combination with said relief valve and pilot valve of snap-acting valve means operably connected to the accumulator and to the control chamber of the relief valve, said snap-acting valve means being operable to vent the control chamber in response to predetermined pressure increases in the accumulator lower than the pilot relief valve predetermined responsive pressure and causing the relief valve to unload the pump.

7. In a hydraulic power transmission system having a pump forming a source of pressure fluid, an accumulator for storing pressure fluid, and a pressure responsive relief valve of the type which is balanced as to opposing pressure forces and having a control chamber ventable at a predetermined pressure for unbalancing the pressure forces and causing the relief valve to by-pass the pump, the combination with said relief valve of a valve for causing the relief valve to unload the pump, said valve comprising a body having a venting port, a control port connected to the control chamber of the relief valve and a pressure port connected to the accumulator, a poppet valve between the control and venting ports, means biasing the poppet valve to close communication between the control and venting ports, and means connected to the pressure port responsive to predetermined pressure increases at said port lower than the first mentioned relief valve predetermined pressure for shifting the poppet valve to open the control port to the venting port thereby causing the pressure forces on the relief valve to become.completely unbalanced and causing the relief valve to unload the pump.

MACKELLAR K GRAHAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

